The separation of convolutive mixtures aims to estimate the individual sound signals in the presence of other such signals in reverberant environments. As sound mixtures are almost always convolutive in enclosures, their separation is a useful pre-processing stage for speech recognition and speaker identification problems. Other direct application areas also exist such as in hearing aids, teleconferencing, multichannel audio and acoustical surveillance.
Our earlier patent application published as WO 2009/050487 discoses a system for separating a mixture of acoustic signals from a plurality of sources which comprises a sensor array comprising a plurality of pressure sensors and a processor arranged to receive signals from the sensors, and derive from them a series of sample values of directional pressure gradient, identify a plurality of frequency components of the signals, and define an associated direction for each frequency component. The system is then arranged to identify a subset of the frequency components with a source, thereby to define an accoustic signal for that source. Signals for several sources can be defined. In order to provide three dimensional source separation, a three dimensional array of sensors can be used, for example a tetrahedral array.
Our further earlier patent application no PCT/GB2013/050784 discloses a microphone array for a system similar to that of WO2009/050487, but in which the array is designed for ease of manufacture. This is achieved by forming the array of support means having two opposite sides and four sensors, with at least one of the sensors supported on each side of the support means, and the sensors facing in directions that are parallel to each other. Because the systems described in WO2009/050487 and PCT/GB2013/050784 work by measuring pressure gradient within the sound wave between different microphones in the array, the arrays described in WO2009/050487 and PCT/GB2013/050784 were designed to allow sound to travel between the microphones as easily as possible, so as to interfere as little as possible with the propagation of the sound wave past the array.